Gazetteer Data

Wilkinson’s Gazetteer and Bibliography of the Mines and Quarries of North Wales


This page describes the background to the data that forms the basis of Jeremy Wilkinson’s Gazetteer and Bibliography of the Mines and Quarries of North Wales. In particular it addresses:

This page does not cover technical aspects of the system. These can be found on the gazetteer READ ME page.

Wilkinson’s Data

As stated on the Gazetteer front page, the Gazetteer and Bibliography data were originally compiled over a considerable number of years by Jeremy Wilkinson from Inspectors of Mines reports, Home Office lists of mines and quarries, The Public Record Office (now named the National Archives) and other sources of public record. In addition to the formal documentary sources, Wilkinson searched the second edition of the Ordnance Survey 6" maps (based on surveys from 1899 onwards) and some other maps for unnamed features such as mines, shafts, levels, quarries etc.

Wilkinson created a single record for each site (mine, quarry or other physical feature) he found. Sites with more than one name or where the name changed with time were recorded as a separate site for each name (with, where known, the same grid reference). Sites without documented names such as the mines, shafts, levels, quarries etc. mentioned above were assigned names based on named map features in their vicinity. However, where sites were more or less equidistant from several named features, the choice of name appeared arbitrary.

Wilkinson provided 6-figure British National grid references for sites with known locations. As far as can be ascertained, he recorded the locations by measurement on projections of microfilmed 6" map sheets. Consequently, a number of such locations were found to be in error – though generally not to a significant degree.

In addition to the site records, Wilkinson created reference records for each site. These included references to Home Office Lists of Mines, HM Mine Inspectors’ reports etc. plus some references to secondary sources such as David Bick’s The Old Copper Mines of Snowdonia. For the unnamed sites mentioned above, Wilkinson provided the 6" map county name and sheet number (though in some cases the site was not shown on the map specified but on the corresponding 25" map instead). The references also included some cross-references to other sites.

Product codes, county and parish identifiers etc., which were used to reduce space in the site and other files, were translated to actual county etc. names by Wilkinson’s display programs using data embedded in the programs.

Wilkinson’s main interest appears to have been the metalliferous mines and slate quarries of north-west Wales. Consequently, his coverage of north-east Wales, particularly with regard to coal mining, is less comprehensive than for other areas.

Copies of Wilkinson’s original files have been kept for archival purposes.

File Structure

Wilkinson’s fixed record length files have been converted to variable length records and record structures have been altered as a consequence. However, the general organisation of the main data files and the relationships between them is substantially unchanged from Wilkinson’s system as it stood in 2002.

The translations of product codes, county and parish identifiers etc. were extracted as strings from Wilkinson’s BASIC program files and used to create separate files.


The term ‘Site’ encompasses mines, quarries, levels, trials etc. together with some non-extractive related sites such as slate mills remote from quarries, smelters etc.

Site Names

There is considerable variation between sources as to site names. To handle this:

Duplicated data have been eliminated and minor corrections have been made.

Wilkinson’s data included a approximately 1600 sites with no documentary evidence for their names. These were mostly small quarries and gravel pits (typically used for building or road materials), isolated shafts etc. Wilkinson assigned names to these sites based on nearby features (typically topographic or farm names). It was decided to revert them to just that shown on the map. The facility to search by distance from a specified grid reference, latitude/longitude or post code allows such unnamed sites near a given location to be displayed.

GB1900 data

To ensure comprehensive coverage, data have been included from The University of Portsmouth GB1900 Gazetteer project. This is a crowd-sourced catalogue of all named features on the 2nd edition OS 6" maps. The data were processed to extract all mining and quarrying related features (levels, mines, quarries, pits, etc.) together with their county, administrative district and grid reference. Feature names were converted to the form used elsewhere in the gazetteer so that, for instance, ‘Old Gravel Pit’ would be converted to ‘PIT’ with the product code for gravel.

A problem with the GB1900 data is that the grid references in most cases appear to be that of the start of the text associated with a map feature rather than the feature itself. (This is understandable as it presumably avoided the need for subjective interpretation of the map by the data compilers.) However, because the existing gazetteer data records the grid reference of the sites themselves, it has caused problems with merging the GB1900 data with the existing gazetteer data in that it is not easy to distinguish between what are multiple records for the same site (i.e. alternative names), specific features of the same site which are recorded separately (e.g. Level, Shaft etc.) and what are separate but nearby sites. This is a particular problem in the Halkyn area. A utility was developed to identify clusters of sites for examination and the map checked for each cluster to eliminate redundant records. Where is was not possible to associate map features such as shafts with specific mines, the individual records for such features were retained.

National Grid References

The site data file has been reformatted to allow the use of 8-figure grid references if so desired. Grid references for additional sites and corrections to grid references in existing data where encountered have been corrected by reference to National Library of Scotland georeferenced versions of the 2nd edition OS 6" maps (or, in some cases 25" maps). Such corrections been made in accordance with The National Grid Map Reference System, Ordnance Survey 2004 i.e. the grid reference specifies the south-west corner of the 1 km (4-figure references), 100 m (6-figure references) or 10 m (8-figure references) grid square in which the feature is shown on the map.

Extensive sites such as the Penrhyn and Dinorwic slate quarries have 4-figure (i.e. 1 km precision) grid references. New records of small sites such as individual shafts have been given 8-figure (i.e. 10 m precision) grid references.

Calculations of distances between grid references and conversions from grid references to latitude-longitude coordinates (as used for indicating locations on online maps) are made from the centre of the grid square (1 km, 100 m or 10 m) as indicated by the number of digits in the grid reference.

Sites with identical grid references are automatically cross-referenced. When the cross referenced site has references additional to those already shown in the current gazetteer entry, the name of the cross referenced site is presented as a link to that site (otherwise the site name is just presented as plain text).

Map-related facilities

Ordnance Survey grid references are presented as links to their location on the UK Streetmap website 1:25,000 OS map.

Gazetteer entries for sites with known locations include links to the location on NLS 2nd edition (c. 1900) georeferenced maps, Zoom Earth and Google maps.

Gazetteer references to specific OS 6" and 25" map sheets are shown as links to the appropriate NLS sheet image.

The site search ‘display as map’ option allows the display of the location of all sites found on a map. This allows the distribution of sites matching the search criteria to be seen. Named sites are shown with a larger marker than that used for the unnamed sites. Non-extractive sites are shown on the map display with blue markers rather than the red markers used for extractive sites.

Employment and production data

A facility to include employment (men employed above and below ground by year) and production (product output by year) data for sites has been implemented. However, as of October 2020, such data has been entered for only a few sites; more will be added as time permits.

Non-extractive sites

The following non-extractive sites are considered to be of relevance to the gazetteer and have been added to the data:


The term ‘Entity’ encompasses individuals, partnerships, private companies, limited companies and other organisations.

A consequence of Wilkinson’s fixed record length files was than some company and individual names were truncated. Such truncated names have been corrected where possible or else marked as ‘[possible name completion?]’


Individuals with common surnames and forenames or initials have been given separate entries except where it is obvious from context (role at a site or in a company, dates of activities etc.) that they refer to the same individual. Where forenames were given in full in some instances and in others as initials only and it was obvious that they refered to the same individual, they are presented as the full name.

Titles, ranks and other honorifics are included in the data but are ignored for the purposes of searches.

Limited Companies

Where there are variations in the spelling of the names of Limited companies, the company name as shown on the UK National Archives website has been considered to be the definitive version.

Some company names recorded in Home Office List of Mines etc. do not accord exactly with the registered name of a company. Where the identity is clear the UK National Archives version has been used.

A facility to add company information to the data has been implemented. Wilkinson provided a number of ring binders of hand-written summaries of company records. The summaries include the Company Registered Addresses, Main Objects Clauses and lists of directors, shareholders, company secretaries etc. As of May 2021, information has not been entered for all limited companies; more will be added as time permits. (It should be noted that some of Wilkinson’s longhand transcriptions are difficult to read and users should be aware that errors may have been introduced in this process.)

Other Features


Spellings of Welsh place and site names etc. have been kept as shown in the original documents.

Additional Data

Although Wilkinson’s data originally referred to the mines and quarries of the pre-1974 counties of north Wales (Anglesey, Caernarfonshire, Denbighshire, Flintshire and Merionethshire), some additional sites such as slate quarries in Montgomeryshire to the east of Afon Dulas and collieries in the continuation of the north-east Wales coalfield into north-west Shropshire have been incorporated.

References to a number of secondary sources have been added, in some cases with the creation of additional site and entity records. This has been done so as to improve the coverage of the gazetteer and because in many cases such sources are more accessible than the primary sources.

The bibliography does not claim to be exhaustive. Further information on limited companies may be found in National Archives and The London Gazette, both of which are searchable on-line. The National Library of Wales newspaper archive, also searchable online, is a useful resource, particularly for notices of sales of quarries etc. and reports of fatal accident inquests.


Where information further to that currently visible, names of sites, individuals, companies etc. are shown as links to the specific information for the site or individual etc. concerned. Thus, if the information exists, it is possible to search for a specific mine and then follow the link for, for instance, an agent at that mine to see what other mines (with links to them) he was associated with and what his roles were at them.

In addition to the automatic presentation of cross references described above, the system has facility for the manual inclusion of plain text notes and additional cross references such as indication of underground connections between mines or underground slate quarries.

Data integrity

A site maintenance tool is used to test for inconsistencies in the data such as duplicate identifiers, badly formed or missing data etc. This is employed before uploading amended data to the public server.

Sources of error

The following possible sources of error should be considered:

As far as the online gazette is concerned, efforts has been made to avoid introduction of additional errors during its compilation. However, with a work of this kind it is unlikely that it is entirely free of error and the disclaimer below should be heeded.


As of 1st March 2021 the gazetteer has:

Supporting the above are:


The gazetteer makes no claim to be exhaustive nor entirely free from errors. Whilst the gazetteer provides a useful starting point for historical research on the nineteenth- and early twentieth-century extractive industries of north Wales, users should refer to the primary sources cited if considering detailed research and publication.

See also the disclaimer on the Hendrecoed North Wales Mining History website front page.

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